Low inertia motor for fluid operated tool

ABSTRACT

A rotary vane expansible chamber fluid motor having a rotor member constructed with relatively large axially extending grooves formed between the radially extending vanes. The moment of inertia of the rotor member is substantially less than a comparable cylindrical rotor and the expansible chamber volume is greater than a conventional rotary vane motor. The motor is advantageously used in fluid operated tools for tightening threaded fasteners.

United States Patent Sorensen et a1.

LOW INERTIA MOTOR FOR FLUID OPERATED TOOL Inventors: Clarence A. Sorensen, Fruitport; Edwin J. Deremo, Spring Lake, both of Mich.

Assignee: Gardner-Denver Company, Quincy,

Filedz Feb. 4, 1971 Appl. No.: 112,773

Related US. Application Data Continuation of Ser. No. 818,957, April 24, 1969, abandoned.

US. Cl. ..4l8/270 Int. Cl. ..F0lc 13/02 Field of Search..-......4l8/270, 82, 124, 155, 159,

References Cited UNITED STATES PATENTS 2/1900 Craig ..4l8/82 8/1911 Curtis ..418/82 8/1955 Sturrock ..418/159 9/1956 Adams et a1. ..4l8/267 X [451 Oct. 24, 1972 Primary Examiner-Everette A. Powell, Jr. Attorney-Michael E. Martin [57] ABSTRACT A rotary vane expansible chamber fluid motor having a rotor member constructed with relatively large axially extending grooves formed between the radially extending vanes. The moment of inertia of the rotor member is substantially less than a comparable cylindrical rotor and the expansible chamber volume is greater than a conventional rotary vane motor. The motor is advantageously used in fluid operated tools for tightening threaded fasteners.

2 Claims, 6 Drawing Figures PATENTED um 24 I972 SHEET 2 [IF 2 1.0 rnrnr flanaLarahrm sattmds 1 LOW INERTIA MOTOR FOR FLUID OPERATED TOOL This application is a continuation of application Ser. No. 818,957 filed Apr. 24, 1969, now abandoned.

BACKGROUND OF THE INVENTION in automotive parts assembly operations to control the torque applied to the fastener within precise limits to assure that a safe and reliable structure is produced. These assembly tools usually employ a rotary vane expansible chamber motor driving a wrench socket or screwdriver bit through a speed reduction gear transmission. Rotary vane air motors are extensively used in power tools because they are simple and compact in design and although they do not exhibit the most desirable torque output characteristics their low cost of manufacture and high reliability in service make them a logical choice for use in tools which must withstand long and rigorous service. In order to make fluid operated power tools using rotary vane motors more versatile and applicable to a greater range of output torques, interchangeable gear transmissions are used to allow the motor to operate at selectable speeds which will produce smooth turning effort and still produce a desired range of torque at the tool output spindle.

One longstanding problem encountered in the use of conventional rotary vane air motors in power wrenches and screwdrivers is the elimination of the effect of the kinetic energy of the tool motor rotor member which is transformed into torque exerted on the fastener as a result of rapid motor deceleration. It is desirable in specifying the maximum output torque of a pneumatic tool to consider basically the torque produced by the motor at the stalled condition which is a function of the unbalanced pressure force exerted by the operating fluid on the motor multiplied through the gear drive, if used. However, in accordance with the laws of mechanics dealing with changes in momentum of rotating bodies the smaller the deceleration time, the greater the unbalanced torque produced by the transformation of kinetic energy from the rotating member to the fastener. The problem of rapid motor deceleration is particularly acute when securing joints which have what is known as a hard make-up. The torque exerted by the tool due to transformation of kinetic energy from the motor rotor to the fastener under rapid deceleration can often result in damage to the tool or overstressing the fastener to the point of structural failure. Also, the total torque produced by the tool becomes a function of joint make-up characteristics which are difficult to control in mass production assembly operations.

Another problem in tightening threaded fastener joints is encountered in joints which have what is known as a soft makeup." Such joints are typified by those having thick gaskets interposed between two rigid members or comprisinga resilient member as one of the members being joined, e.g.,'a rubber bushing or a vibration dampening engine mount. In tightening joints having a soft make-up, dissipation of the kinetic energy of the rotor is not a problem since the time span for approaching the motor stall condition is substantially greater than for a hard make-up joint which results in relatively insignificant values of unbalanced torque being exerted on the fastener due to the change in momentum of the motor rotor. However, another problem with rotary vane motors is that they exhibit poor running characteristics at slow speed due primarily to internal leakage of pressure fluid.

SUMMARY OF THE INVENTION The present invention provides a rotary vane expansible chamber motor having a rotor member constructed to provide a substantially'reduced mass moment of inertia whereby in a power tool for tightening threaded fasteners the novel motor construction largely eliminates the kinetic energy effect on achieving a predetermined tool output torque. In contradistinction to conventional rotary vane motors designed for use with expansible working fluids, the present invention provides a rotor member for a rotary vane motor which provides for greater expansible chamber volume and, accordingly, a reduced motor expansion ratio. Such increased chamber volume combined with a reduced expansion ratio improves slow speed torque output of a motor due to the fact that a higher average unbalanced pressure force operates to turn the motor. By constructing a rotor member comprising primarily a hub portion and radially extending flanges to form vane slots, there is provided a fluid operated rotary vane motor having improved acceleration and deceleration characteristics and greater low speed turning effort than heretofore known.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 isa partial sectional view of a typical fluid operated power wrench utilizing the motor of the in-' stant invention.

FIG. 2 is a transverse section taken along the line 2- 2 of FIG. 1 illustrating the configuration of the improved rotary vane motor.

FIG. 3 is a transverse section of a conventional rotary vane fluid motor.

FIG. 4 is a sectional view of a typical hard makeup threaded fastener joint.

FIG. 5 is a sectional view of a typical soft make-up threaded fastener joint.

FIG. 6 is a graphical comparison of the torque produced by the kinetic energy of the rotor member of the rotary vane motor of the present invention and a conventional motor.

DESCRIPTION OF THE PREFERRED EMBODIMENT Numerous types of fluid operated tools for tightening threaded fasteners may advantageously utilize the present invention. A typical tool powered by compressed air is illustrated in FIG. 1 and generally designated by the numeral 10. The tool 10 includes a housing 12 having a handle portion 14. Located within a bore 16 of the tool housing 12 is a fluid operated rotary vane motor 18. The motor 18 includes a casing 20 having a substantially cylindrical longitudinal chamber 22 which has a longitudinal axis eccentric to the outer diameter 24 of the casing. The motor 18 also includes end plate members 26 and 28 closing the ends of the chamber 22. The motor casing and end plate assembly is retained in the housing-12 by a nut 30.

The motor 18 also comprises a rotor member 32 which is rotatively supported in the cylindrical chamber 22 by bearings 34 and 36 located in the end plates 26 and 28, respectively. The rotor member 32 includes a shaft portion 38 having a gear 40 formed integral therewith. The rotor shaft 38 extends into a gear housing 42 attached to the tool housing 12 by a nut 44. The gear housing 42 also comprises a fixed annular gear 46 of a planetary gear transmission which further includes planet gears 48, one shown, which are engaged with the gear 40, and are mounted on a rotatable planet carrier 50. The planet carrier 50 is nonrotatably connected to a drive shaft 52 which in turn rotatively drives the tool drive spindle 54 located in the angle drive attachment 56. The spindle 54 is operable to be connected to a wrench socket or screwdriver bit in a manner well known. In accordance with known design practices, various gear transmission units having different speed ratios may be interchanged in the tool to provide a desired output speed and torque at the spindle 54.

Pressure fluid to operate the motor 18 is supplied to the tool from a source not shown through a supply line 58 attached to the handle portion 14 and in communication with the passage 60. An operator actuated control valve 62 is operable to valve fluid from the passage 60 through the hollow valve seat 64, and passages 66 and 68 to the motor inlet port 70. Exhausting of spent motive fluid from the motor 18 is provided by exhaust ports 72 in the casing which open into the annular area 74. Exhaust fluid can flow from area 74 through passage 76, and space 78 in the gear housing 42, and passages 80, to a muffler 82 which communicates with the exterior of the tool.

The exemplary tool illustrated in FIG. 1 operates to tighten a threaded fastener until the torsional resistance to turning of the fastener exceeds the maximum torque output of the motor multiplied through the gearing and the motor therefore stalls. Various control devices may also be used intools of this general type which directly or indirectly sense the torque output of the tool and operate to shut off motive fluid to the motor when a predetermined torque value is achieved. The present invention may be advantageously used in either stall type toolsor the latter types mentioned.

Referring to FIGS. 1 and 2 the rotor member 32 is rotatable about a longitudinal axis 79 eccentric with respect to the axis 81 of the chamber 22 but substantially parallel thereto. The rotor 32 slidably carries a plurality of spaced vane elements 84 in radial slots 86 formed by parallel flanges 88. The vanes 84 are operable to be radially movable into fluid sealing engagethem with the wall of the chamber 22 and are longitudinally dimensioned to be in close proximity to the respective surfaces 90 and 92 of the end plates 26 and 28, FIG. 1, to prevent leakage of pressure fluid therebetween. Adjacent vanes form with the chamber 22 and the rotor member 32 expansible chambers 94 which, in a manner well known, are operable to receive pressure fluid through the inlet port 70 whereby unbalanced pressure forces acting on the vanes 84 operate to turn the motor rotor 32 in the direction indicated by the arrow in FIG. 2. As the rotor 32 rotates the expansible chamber volume increases and the fluid expands until a chamber 94 is in communication with the exhaust port 72 whereby fluid is exhausted from the motor. The ports and 72 may, of course, be positioned such that no actual expansion of fluid-and, accordingly, no reduction in pressure occurs before the chambers 94 are in communication with the exhaust port.

FIG. 3 illustrates in cross section a conventional rotary vane motor 96 having a casing 98 with a cylindrical chamber 100 similar to the motor 18 of FIGS. 1 and 2. The rotor of the motor 96 comprises a cylindrical member 102 eccentrically mounted with respect to the axis of the chamber 100 and having a plurality of radial vanes 104 slidable in slots 106. Adjacent vanes fonn, with the chamber 100 and the rotor 102, expansible chambers 107. An inlet port 108 and exhaust port 110 are also provided, as in the motor 18.

In contradistinction to the prior art rotor member 102 of FIG. 3, the rotor member 32 of FIGS. 1 and 2 provides a wall surface relieved radially inwardly away from the radial extremities 89 of the vane support flanges 88. This surface relief is provided by longitudinal grooves 91 intermediate adjacent vane support flanges; and, the relieved surfaces comprise a portion of the boundary wall of the'expansible chambers 94. Whereas in the prior art rotor 102 a solid cylinder is formed, except for the vane slots, in the rotor 32 an imaginary surface of revolution is formed by the extremities 89 and designated by the dotted line 93. The surface relief away from the imaginary surface of revolution 93 formed by the grooves 91 has been found to provide improved operating characteristics of fluid operated motors used in power wrenches and the like. It is also a characteristic of prior art cylindrical rotors to provide for a fluid seal between the inlet port and the exhaust port by the close spacing of the rotor cylinder to the chamber wall as indicated by the numeral 97 in FIG. 3. In the motor 18, however, a more positive seal is provided by placing the inlet port and exhaust port so that a vane 84 is always interposed therebetween regardless of rotor position.

A distinct advantage of employing the rotor member 32 in a pneumatic tool such as a nutsetter or screwdriver is the reduction in kinetic energy of the tool rotating mass of which, in a typical power tool, the motor rotor comprises approximately to percent, the remainder comprising the gearing, drive shaft and spindle. The high percentage of kinetic energy possessed by the motor rotor is due to its large mass and high rotative speed in comparison with the remainder of the tool rotating components. It is common to provide rotary vane motors in power tools which operate at speeds of 10,000 to 30,000 r.p.m. whereas these speeds are reduced to 200 to 1,400 r.p.m. at the tool drive spindle. The physical principles describing the rotational motion of bodies are well known and will not be dealt with in detail herein. However, by reducing the mass moment of inertia of a body rotating about an axis the kinetic energy which must be dissipated upon arresting the rotation of said body is proportionately reduced. By way of example, a steel rotor approximately 1.1 inches in diameter by 2.0 inches long having a 88 advantageously eliminate rotor mass at the greatest radial distance from the axis of rotation 79.

FIG. 6 illustrates graphically the amount of overtorquing caused by kinetic energy dissipation of the two rotor members described above. The horizontal scale is logarithmic and represents rotor deceleration time in seconds. The vertical scale is linear and represents torque in pound-feet. The curve 112 representsthe amount of torque produced on the fastener as a function of the deceleration time of the cylindrical prior art rotor. The curve 1 14 represents the torque produced by the rotor member 32 of the same size and material as the prior art rotor. The vertical scale of the graph of FIG. 6 represents torque values over and abovethe maximum torque which can be produced by the unbalanced pressure forces acting on a motor at the rotor stalled condition.

Referringto FIG. 4 an extreme example of a socalled hard make-up joint is illustrated. The joint of FIG. 4 comprises a substantially rigid member 116 whichissecured to a second rigid member 118 by a threaded fastener 120 with a plain nonlocking hard metal washer 122. In this joint the rigidity of the joint itself is much higher than the rigidity of the fastener. In actual practice the joint rigidity would be somewhat less than the example of FIG.4. However, by way of example, typical so-called hard make-up joints for a 5/16 inch diameter bolt having eighteen threads per inch will cause motor deceleration times as rapid as 0.070

seconds, depending on spindle rotational speed. The

time factor represented by the horizontal scale of FIG. 6 is the elapsed time from the beginning of deflection of the joint being made up until the tool motor stalls and does not include the so-called free run-down portion of the cycle. As can be seen from FIG. 6 overtorquing of the fastener under such rapid motor deceleration would amount to approximately 5.6 lb. ft., with the prior art cylindrical rotor represented by curve 112 whereas an oveitorque of only 1.8 lb. ft. would be encountered with the rotor member according to the present invention represented by curve 114. Accordingly, the rotor member 32 provides for tightening threaded fastener joints within a much narrower range of specified torque tolerances as well as reducing stresses on the tool drive component such as gears, shafts and bearings.

FIG. 5 illustrates a typical so-called soft make-up joint, commonly found in the design of mechanical joints, comprising substantially rigid members 124 and 126 joined together with a resilient gasket member 128 interposed therebetween. The joint of FIG. 5 also includes a helical spring lock washer 130 under the head of the fastener 132 securing the joint. in tightening the fastener 132 of the joint of FIG. 5 with a pneumatic tool such as the tool 10 the dissipation of the kinetic energy of the motor rotor and other rotating members is less of a problem because the deflection of the joint 6 caused by the gasket 128 and the spring washer 130 will cause a relatively slow buildup of torsional resistance to turning of the fastener and hence a relatively slow approach to the stalling torque of the motor. Typical soft make-up joints using the fastener previously described will usually reach motor stalling torque in elapsed times of 0.30 seconds or greater depending on tool spindle speed. As can be seen from FIG. 6, the lower rate of dissipation of kinetic energy of the motor rotor results in less overtorquing for both the prior art rotor and the rotor member 32. However, the curve 114 representing the present invention indicates overtorque values appreciably lower than a standard cylindrical rotor regardless of rotor deceleration time. Oven torquing resulting from kinetic energy dissipation approaches a negligible value as the elapsed time to stall the motor approaches 10.0 seconds.

In further contradistinction to the teaching in the art of expansible chamber fluid motors, the rotor member 32 of the motor 18, due to the surface relief formed by the grooves 91, provides increased volume of the expansible chambers 94 compared with the chambers 107 of the rotor 102. Therefore, a reduction in the change in expansible chamber volume occurs between the position where a chamber is closed off from the inlet port by the sealing of the trailing vane tip and the position where the chamber is open to the exhaust port. However, in expansible chamber fluid motors used for developing torque at low speeds such as the application of tightening threaded fasteners it is desirable to maintain a high unbalanced pressure force operable to turn the motor rotating member so that greater torque is available at the tool spindle on approach to the stall condition. Due to the increased volume provided by the grooves 91, the expansible chambers 94 of the motor 18have received a greaterquantity of fluid at inlet pressure than is possible for the chambers 107 of thepriorart motor 96. In a rotary vane motor such as the'rnotors 18 and 396 leakage of pressure fluid out of the expansible chambers occurs primarily between the end plate surfaces and 92 and the respective adjacent end surfaces of the vanes. This leakage area may be dimensionally flxedfor a given size motor and there fore comprises a fixed orifice for controlling leakage flow. In accordance with the laws governing the behavior of gases the reduction in pressure due to leakage flow out of chambers 94 of the motor 18 will be less than for the prior art motor 96. Furthermore, the added volume of chambers94 provided by the grooves 91 contributes to maintaining high pressure of the fluid trapped therein by reducing the change in volume of said chambers as the rotor moves from communication of the chambers with the inlet port to the exhaust port. The unbalanced pressure force acting on vanes 84 and the resultant output torque, particularly at low speed, will therefore be greater for motor 18.

Fluid operated tools using the motor 18 may be reliably used to produce a predetermined output torque for a given motor supply pressure of the working fluid based on joint make-ups considered to be flexible or soft. These same tools may then be used on relatively hard make-up joints without concern for variations in torque output due to the fact that overtorquing resulting from motor rotor kineticenergy dissipation is substantially reduced. Accordingly, more consistent torque values may be obtained regardless of the variables, controlled or uncontrolled, which affect mechanical joints.

What is claimed is:

1. In a fluid operated tool for tightening threaded fasteners:

a housing;

a rotary vane expansible chamber fluid motor in said housing including a cylindrical chamber, fluid inlet and exhaust ports in communication with said chamber, and a rotor member supported in said chamber and operable to be rotatively driven about an axis of rotation which is eccentric with respect to the longitudinal axis of said chamber by pressure fluid supplied to said chamber, said rotor member including spaced apart radially extending vane means forming with said rotor member and a wall of said chamber movable expansible chamber means operableto be in and out of communication with said inlet and exhaust ports;

rotatable drive means connected to said rotor member and operable to be connected to a threaded fastener for rotatively driving said threaded fastener in response to pressure fluid being supplied to said motor, and the improvement characterized by:

said rotor member having longitudinal grooves defined by radially relieved exterior wall surfaces intermediate said spaced apart vane means, said.

grooves extending the length of said rotor member for reducing the rotational moment of inertia of said rotor member, and said grooves forming a portion of said expansible chamber means for receiving pressure fluid when said expansible chamber means are in communication with said inlet port whereby pressure fluid received in said portion from said inlet port causes an unbalanced pressure force acting on said rotor as said expansible chamber means move from communication with said inlet port to communication with said exhaust port for increasing the slow speed turning effort of said rotor.

2. The invention set forth in claim 1 wherein: said grooves are formed by adjacent radially extending flanges comprising means forming slot means for receiving said vane means. 

1. In a fluid operated tool for tightening threaded fasteners: a housing; a rotary vane expansible chamber fluid motor in said housing including a cylindrical chamber, fluid inlet and exhaust ports in communication with said chamber, and a rotor member supported in said chamber and operable to be rotatively driven about an axis of rotation which is eccentric with respect to the longitudinal axis of said chamber by pressure fluid supplied to said chamber, said rotor member including spaced apart radially extending vane means forming with said rotor member and a wall of said chamber movable expansible chamber means operable to be in and out of communication with said inlet and exhaust ports; rotatable drive means connected to said rotor member and operable to be connected to a threaded fastener for rotatively driving said threaded fastener in response to pressure fluid being supplied to said motor, and the improvement characterized by: said rotor member having longitudinal grooves defined by radially relieved exterior wall surfaces intermediate said spaced apart vane means, said grooves extending the length of said rotor member for reducing the rotational moment of inertia of said rotor member, and said grooves forming a portion of said expansible chamber means for receiving pressure fluid when said expansible chamber means are in communication with said inlet port whereby pressure fluid received in said portion from said inlet port causes an unbalanced pressure force acting on said rotor as said expansible chamber means move from communication with said inlet port to communication with said exhaust port for increasing the slow speed turning effort of said rotor.
 2. The invention set forth in claim 1 wherein: said grooves are formed by adjacent radially extending flanges comprising means forming slot means for receiving said vane means. 